1. Field of the Invention
The present invention relates to an airbag suitable for use in a knee-protecting airbag apparatus for protecting knees of a seated driver in the event of impact of vehicle.
2. Description of the Related Art
JP2003-291761A discloses a conventional airbag for protecting knees of a driver by FIGS. 5 and 6. This airbag is folded up and housed in a lower area of a space in front of knees of a seated driver. The airbag has a gas source in the lower area as fully inflated, which lower area constitutes an upstream portion of inflation gas whereas the upper area as fully inflated constitutes a downstream portion of inflation gas. When fed with inflation gas, this airbag emerges from the housing toward the rear and deploys upward in such a manner as to cover the lower surface of the column cover which extends obliquely upward and rearward. The airbag includes on the left and right of the upper area facing away from the gas source knee-arresting portions inflatable to have enough thicknesses to cushion both knees. Below and between the left and right knee-arresting portions is a thickness-regulating tether that connects the driver-side wall and column cover side wall of the airbag that helps inflate the airbag in a plate fashion. The airbag further includes at the center in a left and right direction on the upper edge as fully inflated an accommodating recess that recesses downward for accommodating the underside of the column cover.
In the above conventional airbag, materials forming the driver-side wall and column cover side wall each has on the upper edge a recess that constitutes the accommodating recess, and the airbag is manufactured by connecting such materials together at outer peripheral edges by sewing or the like.
That is, manufacturing of the above conventional airbag involves cutting materials for forming the driver-side wall and column cover side wall in a curved manner for forming the recesses and sewing the materials in a curved fashion, which is troublesome.
Especially in the above airbag, whenever inflation gas flows through the upper area of the airbag (which is located on downstream of gas channel), hot and high-pressure gas flows along the upper edge of the airbag and hit the seam of the accommodating recess that recesses inward of the airbag. Considering this, double stitching has been applied to the seam to enhance durability, and which has further complicated manufacturing.
Moreover, if the inflator located in the lower area of the airbag has gas discharge ports at one side in a left and right direction, the gas exited the inflator firstly pushes the upper edge of the airbag at the side where the discharge ports are located and then flows toward the other side. If the materials forming the airbag are provided with recesses in the upper edge, the force of the gas that pushes the upper edge of the airbag at the side of the discharge ports is enhanced and thereby causing an imbalanced inflation in a left and right direction of the airbag.